1. Field of the Invention
The present invention relates to a reset signal generation circuit which outputs a reset signal at the time of a voltage being decreased to a processing device which operates according to a voltage applied from a power circuit.
2. Description of the Related Art
In the related art, there have been known reset signal generation circuits having a configuration capable to continue resetting until a power voltage reaches a higher voltage at the time of being powered on and capable of preventing resetting until the power voltage becomes a low voltage to an extent that operation is not hindered at the time of the power voltage being decreased (for example, refer to JP 11-31956 A). In the reset signal generation circuit, when the power voltage exceeds a first voltage (reset release voltage), outputting of a reset signal is stopped, and after that, when the power voltage is equal to or lower than a second voltage (reset detection voltage) which is lower than the first voltage, the reset signal is output again. In this manner, a voltage which generates the reset signal is allowed to have hysteresis, and thus, it is possible for a processing device such as an LSI to secure stable operations.
In the reset signal generation circuit disclosed in JP 11-31956 A described above, the first and second voltages are set in a range which is higher than an operation guarantee voltage of the processing device and is lower than the power voltage in a normal operation period. However, recently, the power voltage becomes a low voltage (for example, 3.3 V), and thus, if a variation of the power circuit is considered, there is a tendency that the range becomes narrow. On the other hand, with respect to a difference between first and second threshold voltages, if stability of operation is considered, a certain value needs to be secured. For this reason, when the first voltage is set to be included in a range which is higher than the operation guarantee voltage of the processing device and is lower than the power voltage in the normal operation period, the second voltage is lower than the operation guarantee voltage, and thus, there is a problem in that the operation may not be stable. For example, in the case where the power voltage is lower than the operation guarantee voltage and, after that, is increased again to exceed the operation guarantee voltage, since a result of a process in the time period when the power voltage is lower than the operation guarantee voltage is reflected on the following process, abnormal operation or malfunction occurs.